Sweeteners may be defined as flavor enhancers and food additives for a sweet taste, and typically refer to saccharides of carbohydrate excluding dietary fiber and food additives with high sweetness. The most representative sweetener is sugar, and for the past scores of centuries, humans were accustomed to the sweet taste of sugar. Sugar, which is a disaccharide where glucose and fructose are linked by α-1,2 linkage, greatly contributes to processed foods by enhancing flavor, color and gloss, increasing preservability, etc., as well as providing ideal sweetness to foods with lower costs.
However, the major causes for obesity and diabetes, which suddenly increase these days, are associated with an over intake of high calorie foods containing a large amount of sugar according to the improved standards of living. Accordingly, terms ‘low-calorie food agent’ or ‘health functional,’ etc., emerge as keywords for new product development in the food industry. Particularly, the efforts to reduce calorie lead to development of sugar substitutes with high sweetness, lower (non) calorie, functionality, and also movement of expansion to global food materialization and commercialization.
Sweetening agents which are substituted with natural sweeteners such as sugar, glucose, and fructose and used for the preparation of processed foods may be classified into (i) high intensity sweeteners (e.g., stevioside, aspartame, etc.), with considerably high relative sugar content, which can contribute to the lowering of calorie, (ii) indigestible non-calorie sweetening agents (e.g., sucralose, etc.), and (iii) functional sweetening agents (e.g., sugar-alcohols such as xylitol, oligosaccharides, etc.), which were developed to satisfy health oriented consumption needs through regulation of risk factors against lifestyle-related diseases. The reports that an over intake of sugar may cause lifestyle-related diseases such as obesity and diabetes, further increase the concerns on these sweetening agent substitutes, which results in expansion and growth of the relevant market. Also, consumers' strong desire for wellbeing, health foods for the purpose of prevention of lifestyle related diseases leads to movement of attempting to apply sweetener substitutes in foods with high sugar content. Accordingly, in Korea, various studies attempting to apply sugar substitutes to processes for preparing confectionery, bakery, rice cake, and beverages are presented on muffins and breads with xylitol added, jellies with functional sugar-alcohols and oligosaccharides added, citrus tea with xylitol and erythritol added, cakes with sweetener substitutes added for diabetes patients, rice cakes with trehalose added, beverages with sweetener substitutes having higher sweetness and lower calorie applied, etc.
Sugar is applied to various foods, while serving in processed foods as not only a sweetener providing a sweet taste, but also a functional agent with physiochemical characteristics which provides preferable properties to final products. In other words, sugar not only provides a sweet taste, but also may (i) provide moisturizing effect to products due to excellent moisture absorbing properties derived from hydroxyl groups, (ii) regulate the properties of starch-containing foods depending on use amount and time during process, and (iii) provide properties and sensual characteristics to products by producing coloring and flavor ingredients by maillard reaction with ingredients containing amino groups and caramelization due to thermal treatment. Thus, the application of sweetener substitutes to processed foods is in need of examination on physiochemical changes in final products and sensual characteristics consumers feel, not simple quantitative substitutes taking into account relative sugar content.
Accordingly, while researching and developing optimization in production of non-phosphorylated hexoses which have drawn attention as a natural, functional sweetener substitute substitutable with existing sweeteners such as sugar, glucose, and fructose, etc., the present inventors confirmed that thermophile-derived sugar epimerases are very effective in epimerization of non-phosphorylated hexoses and completed the present invention.